package org.apache.lucene.search.spans;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * Expert: an enumeration of span matches. Used to implement span searching.
 * Each span represents a range of term positions within a document. Matches are
 * enumerated in order, by increasing document number, within that by increasing
 * start position and finally by increasing end position.
 */
public interface Spans {
	/** Move to the next match, returning true iff any such exists. */
	boolean next() throws IOException;

	/**
	 * Skips to the first match beyond the current, whose document number is
	 * greater than or equal to <i>target</i>.
	 * <p>
	 * Returns true iff there is such a match.
	 * <p>
	 * Behaves as if written:
	 * 
	 * <pre>
	 * boolean skipTo(int target) {
	 * 	do {
	 * 		if (!next())
	 * 			return false;
	 * 	} while (target &gt; doc());
	 * 	return true;
	 * }
	 * </pre>
	 * 
	 * Most implementations are considerably more efficient than that.
	 */
	boolean skipTo(int target) throws IOException;

	/** Returns the document number of the current match. Initially invalid. */
	int doc();

	/** Returns the start position of the current match. Initially invalid. */
	int start();

	/** Returns the end position of the current match. Initially invalid. */
	int end();

}
